Organic light emitting display and driving method thereof

ABSTRACT

An organic light emitting display is driven in a simultaneous (or concurrent) emission scheme. The organic light emitting display includes: a display unit including a plurality of pixels coupled to scan lines, control lines, and data lines; a control line driver for providing control signals to the pixels through the control lines; and a power driver for applying a power at different levels to the pixels of the display unit during a plurality of periods of one frame. The control signals and the power are concurrently provided to the pixels included in the display unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/784,411, filed May 20, 2010, which claims priority to and the benefitof Korean Patent Application No. 10-2009-0071279, filed on Aug. 3, 2009,in the Korean Intellectual Property Office, the entire content of whichis incorporated herein by reference.

BACKGROUND

1. Field

Embodiments of the present invention relate to an organic light emittingdisplay and a driving method thereof.

2. Description of Related Art

Recently, various flat panel displays with reduced weight and volume incomparison to a cathode ray tube have been developed. The various flatpanel displays include a liquid crystal display (LCD), a field emissiondisplay (FED), a plasma display panel (PDP), an organic light emittingdiode (OLED) display, etc.

Among the various flat panel displays, the organic light emittingdisplay, which displays an image using organic light emitting diodesthat emit light by re-combination of electrons and holes, has rapidresponse speed and low power consumption.

Generally, OLED displays can be classified as a passive matrix type OLED(PMOLED) display or an active matrix type OLED (AMOLED) displayaccording to a method of driving the OLEDs.

The AMOLED display includes a plurality of gate lines, a plurality ofdata lines, a plurality of power lines, and a plurality of pixels thatare coupled to the data lines and the power lines and arranged in amatrix form. Also, each of the pixels generally includes an organiclight emitting (EL) device, two transistors, that is, a switchingtransistor that transfers a data signal and a driving transistor thatdrives the EL device according to the data signal, and a capacitor thatmaintains a data voltage corresponding to the data signal.

Such an AMOLED display has a low power consumption, but the intensity oramount of current flowing through the organic light emitting devicevaries according to deviation in threshold voltage among thetransistors, thereby causing display non-uniformity.

In other words, since the characteristics of the transistors provided ineach pixel vary according to variables in their manufacturing processes,it is difficult to manufacture the transistors so that thecharacteristics of all of the transistors in the AMOLED display areidentical, thereby causing deviation in the threshold voltage betweenthe transistors of different pixels.

A compensation circuit that includes a plurality of transistors andcapacitors may be provided in the respective pixels. However, in thiscase, each pixel includes the additional plurality of transistors andcapacitors of the compensation circuit.

More specifically, if the compensation circuit is added in each pixel asdescribed above, additional transistors, capacitors and signal lines forcontrolling the transistors are added in each pixel so that in a bottomemission type AMOLED display, the aperture ratio is reduced andprobability that defects are generated is increased due to the increasedcomplexity in the constituents of the circuit.

Moreover, there is a recent demand for a high-speed scan driving of 120Hz or more in order to remove the screen motion blur phenomenon.However, in this case, a charging time available for each scan line issignificantly reduced. In other words, when the compensation circuit isprovided in each pixel so that additional transistors are provided ineach pixel coupled to one scan line, capacitive load of the scan linebecomes large. Therefore, a high-speed scan driving is difficult to beimplemented.

SUMMARY OF THE INVENTION

Embodiments of the present invention relate to an organic light emittingdisplay that is driven in a simultaneous (or concurrent) emission schemeand is able to perform the threshold voltage compensation of drivingtransistors provided in each pixel, thereby enabling high-speed drivingof the display through simple circuit.

According to an embodiment of the present invention, an organic lightemitting display includes: a display unit including a plurality ofpixels coupled to scan lines, control lines, and data lines; a controlline driver for providing control signals to the pixels through thecontrol lines; and a power driver for applying a power at differentlevels to the pixels of the display unit during a plurality of periodsof one frame. The control signals and the power may be concurrentlyprovided to the pixels included in the display unit.

The organic light emitting display may further include: a scan driverfor supplying scan signals to the pixels through the scan lines; a datadriver for supplying data signals to the pixels through the data lines;and a timing controller for controlling the control line driver, thepower driver, the scan driver, and the data driver.

The scan signals may be applied sequentially to the scan lines for apartial period of the periods of one frame and may be appliedconcurrently to the scan lines during the periods other than the partialperiod.

Widths of the sequentially applied scan signals may be applied at twohorizontal time, two adjacently applied ones of the scan signals beingapplied to be overlapped with each other by one horizontal time.

The data signals may be applied sequentially to the pixels by each ofthe scan lines corresponding to the sequentially applied scan signalsand may be concurrently applied to the pixels through the data linesduring the periods other than the partial period.

The power may include a first power applied to the pixels.

Each of the pixels may include: a first transistor having a gateelectrode coupled to a scan line of the scan lines, a first electrodecoupled to a data line of the data lines, and a second electrode coupledto a first node; a second transistor having a gate electrode coupled tothe first node, a first electrode, and a second electrode; a thirdtransistor having a gate electrode coupled to a control line of thecontrol lines, a first electrode coupled to the second electrode of thesecond transistor, and a second electrode coupled to the first power; anorganic light emitting diode having an anode electrode coupled to thefirst electrode of the second transistor and a cathode electrode coupledto a second power; and a capacitor coupled between the gate electrode ofthe second transistor and the first electrode of the second transistor.

The first to third transistors may be NMOS transistors.

When the first power and the control signals are applied at a high levelto the pixels included in the display unit, the pixels may be configuredto light-emit concurrently at brightness corresponding to the datasignals pre-stored at each of the pixels.

The power may include a first power and a second power, and the firstpower and the second power may be applied to the pixels.

Each of the pixels may include: a first transistor having a gateelectrode coupled to a scan line of the scan lines, a first electrodecoupled to a data line of the data lines, and a second electrode coupledto a first node; a second transistor having a gate electrode coupled tothe first node, a first electrode, and a second electrode; a thirdtransistor having a gate electrode coupled to a control line of thecontrol lines, a first electrode coupled to the first electrode of thesecond transistor, and a second electrode coupled to the second power;an organic light emitting diode having a cathode electrode coupled tothe first electrode of the second transistor and an anode electrodecoupled to the first power; and a capacitor coupled between the gateelectrode of the second transistor and the first electrode of the secondtransistor.

The first to third transistors may be PMOS transistors.

Another embodiment of the present invention is directed to a drivingmethod of an organic light emitting display. The method includes: (a)resetting data voltages applied to respective pixels by concurrentlyapplying a first power, scan signals, control signals, and data signals,having voltage values at respective levels, to the entirety of thepixels that constitute a display unit; (b) storing a threshold voltageof a driving transistor included in the respective pixels byconcurrently applying the first power, the scan signals, the controlsignals, and the data signals, having the voltage values at respectivelevels, to the entirety of the pixels; (c) applying the scan signalssequentially to the pixels coupled to scan lines of the display unit andapplying the data signals to the pixels by each of the scan linescorresponding to the sequentially applied scan signals; and (d)light-emitting concurrently the entirety of the pixels at brightnesscorresponding to the data voltages stored in the respective pixels byconcurrently applying the first power, the scan signals, the controlsignals, and the data signals, having the voltage values at respectivelevels, to the entirety of the pixels.

The driving method may further include: (e) turning off emission of thepixels by concurrently applying the first power, a second power, thecontrol signals, and the data signals, having the voltage values atrespective levels, to the entirety of the pixels and thus lowering avoltage of an anode electrode of an organic light emitting diodeincluded in the respective pixels.

One frame may be implemented through (a) to (d).

The one frame may be a progressively progressed frame and may include annth frame for displaying a left-eye image and an n+1st frame fordisplaying a right-eye image.

An entire time between an emission period of the nth frame and anemission period of the n+1st frame may be synchronized with a responsetime of a shutter glasses.

Each of the pixels may include: a first NMOS transistor having a gateelectrode coupled to a scan line, a first electrode coupled to a dataline, and a second electrode coupled to a first node; a second NMOStransistor having a gate electrode coupled to the first node, a firstelectrode, and a second electrode; a third NMOS transistor having a gateelectrode coupled to a control line, a first electrode coupled to thefirst electrode of the second NMOS transistor, and a second electrodecoupled to the first power; an organic light emitting diode having ananode electrode coupled to the first electrode of the second NMOStransistor and a cathode electrode coupled to a second power; and acapacitor coupled between the gate electrode of the second NMOStransistor and the first electrode of the second NMOS transistor.

In (a), the first power may be applied at a low level, the scan signalmay be applied at a high level, and the control signal may be applied ata high level.

In (b), the first power may be applied at a high level, and the scansignal and the control signal may be applied at a high level,respectively.

In (c), the control signal may be applied at a low level. In (c), widthsof the sequentially applied scan signals may be applied at twohorizontal time, adjacently applied ones of the scan signals beingapplied to be overlapped with each other by one horizontal time.

In (d), the first power may be applied at a high level, the scan signalmay be applied at a low level, and the control signal may be applied ata high level.

With the embodiments as described above, the pixel circuit provided inthe respective pixels of the organic light emitting display includesthree transistors and one capacitor, and the pixels are driven in thesimultaneous (or concurrent) emission scheme. Thereby, the thresholdvoltage compensation and the high-speed driving of the drivingtransistor provided in the respective pixels can be performed with asimple circuit.

Moreover, the embodiments enable improved three dimension (3D) displayperformance through the simultaneous (or concurrent) emission scheme asdescribed in the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, together with the specification illustrateexemplary embodiments of the present invention, and, together with thedescription, serve to explain the principles of the present invention.

FIG. 1 is a block diagram of an organic light emitting display accordingto an embodiment of the present invention;

FIG. 2 is a diagram showing a driving operation in a simultaneous (orconcurrent) emission scheme according to an embodiment of the presentinvention;

FIG. 3 is a diagram showing an example where a pair of shutter glassesfor 3D display is implemented in a progressive emission scheme accordingto a related art;

FIG. 4 is a diagram showing an example where a pair of shutter glassesfor 3D display is implemented in a simultaneous (or concurrent) emissionscheme according to an embodiment of the present invention;

FIG. 5 is a graph comparing the duty ratios that can be obtained in thesimultaneous (or concurrent) emission scheme and the progressiveemission scheme;

FIG. 6 is a circuit view showing a circuit schematic according to oneembodiment of a pixel in FIG. 1;

FIG. 7 is a driving timing diagram of the pixel in FIG. 6;

FIGS. 8A, 8B, 8C, 8D and 8E are circuit diagrams and waveform diagramsfor explaining the driving of an organic light emitting displayaccording to an embodiment of the present invention; and

FIG. 9 is a circuit diagram according to another embodiment of the pixelin FIG. 1.

DETAILED DESCRIPTION

Hereinafter, certain exemplary embodiments according to the presentinvention will be described with reference to the accompanying drawings.Here, when a first element is described as being coupled to a secondelement, the first element may be directly coupled to the secondelement, or may be indirectly coupled to the second element via a thirdelement. Further, some of the elements that are not essential to acomplete understanding of the invention are omitted for clarity. Also,like reference numerals refer to like elements throughout.

Hereinafter, exemplary embodiments according to the present inventionwill be described with reference to the accompanying drawings.

FIG. 1 is a block diagram of an organic light emitting display accordingto an embodiment of the present invention, and FIG. 2 is a diagramshowing a driving operation in a simultaneous (or concurrent) emissionscheme according to an embodiment of the present invention.

Referring to FIG. 1, the organic light emitting display according to oneembodiment of the present invention includes a display unit 130 thatincludes pixels 140 that are coupled to scan lines S1 to Sn, controllines GC1 to GCn and data lines D1 to Dm, a scan driver 110 thatprovides scan signals to the pixels 140 through the scan lines S1 to Sn,a control line driver 160 that provides control signals to the pixels140 through the control lines GC1 to GCn, a data driver 120 thatprovides data signals to the pixels 140 through the data lines D1 to Dm,and a timing controller 150 that controls the scan driver 110, the datadriver 120, and the control line driver 160.

In addition, the pixels 140 of the display unit 130 are positioned onregions defined by the crossings of the scan lines S1 to Sn and the datalines D1 to Dm. The pixels 140 receive a first power ELVDD and a secondpower ELVSS from the outside. Each of the pixels 140 controls the amountof current supplied to the second power ELVSS from the first power ELVDDthrough an OLED included in each pixel corresponding to the datasignals. Then, light having a brightness (e.g., a predeterminedbrightness) corresponding to the data signals is generated in the OLED.

In the embodiment of FIG. 1, the first power ELVDD applied to the pixels140 of the display unit 130 has voltage values at different levelsduring one frame. To this end, a first power ELVDD driver 170 thatcontrols the supply of the first power ELVDD is provided, and the firstpower ELVDD driver 170 is controlled by the timing controller 150.

Moreover, in the embodiment of FIG. 1, the organic light emittingdisplay is driven in a simultaneous (or concurrent) emission schemerather than in a progressive emission scheme. As shown in FIG. 2, thismeans that data is input in sequence during the period of one frame, andafter the input of the data is completed, light emission of the pixels140 in accordance with the data of one frame is performed throughout thedisplay unit 130, including all of the pixels 140.

In the progressive emission scheme according to the related art, theemission is performed in sequence right after data is input in sequenceper scan line. However, in the embodiment of FIG. 1, the input of thedata is performed in sequence, but the emission is collectively orconcurrently performed on the entire display unit 130 after the input ofthe data is completed.

Referring to FIG. 2, the driving steps according to an embodiment of thepresent invention is divided into (a) a reset step, (b) a thresholdvoltage compensation step, (c) a scanning step (a data input step), and(d) an emission step. Herein, (c) the scanning step (the data inputstep) is performed in sequence per the respective scan lines, but (a)the reset step, (b) the threshold voltage compensation step, and (d) theemission step are each performed collectively and simultaneously orconcurrently on the entirety of the display unit 130.

Further, (e) an emission turn-off step may also be included after (d)the emission step.

Here, (a) the reset step, which is a step where the data voltage appliedto each pixel 140 of the display unit 130 is reset, is a period wherethe voltage of the anode electrode of the organic light emitting diodeis dropped below the voltage of the cathode electrode so that theorganic light emitting diode is not light-emitted.

Further, (b) the threshold voltage compensation step is a period wherethe threshold voltage of the driving transistor provided in each pixel140 is compensated for.

Therefore, the signals applied during (a) the reset step, (b) thethreshold voltage compensation step, (d) the emission step, and (e) theemission turn-off step, that is, the scan signals applied to therespective scan lines S1 to Sn, the first power ELVDD applied to therespective pixels 140, and the control signals applied to the respectivecontrol lines GC1 to GCn, are collectively and simultaneously (orconcurrently) applied to the pixels 140 provided in the display unit 130at corresponding voltage levels (e.g., predetermined voltage levels),respectively.

In the “simultaneous (or concurrent) emission scheme” according to theembodiment of the present invention, the respective operation periods((a) to (e) steps) are clearly divided in time. Therefore, the number ofthe transistors of the compensation circuit provided in the respectivepixels 140 and the number of the signal lines that control thereof canbe reduced, such that the pair of shutter glasses for 3D display can beeasily implemented.

When a user wears the “pair of shutter glasses” that switchestransmittance of left eye and right eye between 0% and 100% and sees ascreen displayed on an image display, that is, on the display unit ofthe organic light emitting display, the screen is displayed to the useras a left-eye image and a right-eye image for each frame. As such, theuser sees the left-eye image with only his or her left eye and theright-eye image with only his or her right eye, thereby experiencingthree-dimensional effects.

FIG. 3 is a diagram showing an example where a pair of shutter glassesfor 3D display is implemented in a progressive emission scheme accordingto a related art, and FIG. 4 is a diagram showing an example where apair of shutter glasses for 3D display is implemented in a simultaneous(or concurrent) emission scheme according to an embodiment of thepresent invention.

FIG. 5 is a graph comparing the duty ratio that can be obtained in thecases of the simultaneous (or concurrent) emission scheme and theprogressive emission scheme.

When the screen is displayed in the progressive emission schemeaccording to the related art as aforementioned in the case ofimplementing such a pair of shutter glasses for 3D display, as shown inFIG. 3, the response time (for example, 2.5 ms) of the pair of shutterglasses is finite (e.g., non-zero) so that the emission should be turnedoff during the response time in order to prevent a cross talk phenomenonbetween the left-eye/right-eye images.

In other words, a non-light emitting period during the response time isadditionally generated between a frame (n^(th) frame) where the left-eyeimage is output and a frame (n+1^(st) frame) where the right-eye imageis output. Therefore, the duty ratio of the emission time becomes lower.

In the “simultaneous (or concurrent) emission scheme” according to oneembodiment of the present invention, referring to FIG. 4, thelight-emitting step is collectively and simultaneously (or concurrently)performed on the entire display unit as aforementioned, and thenon-emission period is performed during the periods other than thelight-emitting step so that the non-emission period is between theperiod where the left-eye image is output and the period where theright-eye image is output.

In other words, the emission turn-off period, the reset period, and thethreshold voltage compensation period, which are the periods between theemission period of the n^(th) frame and the emission period of then+1^(st) frame, are non-light emitted so that if the entire time of theabove periods are synchronized with the response time (for example, 2.5ms) of the pair of shutter glasses, there is no need to reduce the dutyratio of the emission time unlike in the progressive emission schemeaccording to the related art.

Therefore, when implementing the pair of shutter glasses for 3D display,the “simultaneous (or concurrent) emission scheme” can improve the dutyratio by the response time of the pair of shutter glasses as compared tothe “progressive emission scheme” according to the related art, makingit possible to improve performance. This is illustrated in the graph ofFIG. 5.

FIG. 6 is a circuit diagram of the pixel 140 in FIG. 1 according to oneembodiment of the present invention, and FIG. 7 is a driving timingdiagram of the pixel 140 in FIG. 6.

Referring to FIG. 6, the pixel 140 according to one embodiment of thepresent invention includes an OLED and a pixel circuit 142 that suppliescurrent to the diode OLED.

The anode electrode of the OLED is coupled to the pixel circuit 142, andthe cathode electrode thereof is coupled to a second power ELVSS. TheOLED generates light having a brightness (e.g., a predeterminedbrightness) corresponding to the current supplied from the pixel circuit142.

In the embodiment of FIG. 1, the pixels 140 that constitute the displayunit 130 receive data signals supplied to the data lines D1 to Dm whenscan signals are supplied sequentially to the scan lines S1 to Sn for apartial period (the aforementioned (c) step) of one frame. However, thescan signals applied to the scan lines S1 to Sn, the first power ELVDDapplied to the pixels 140, and the control signals applied to thecontrol lines GC1 to GCn, having predetermined voltage levels, arecollectively and simultaneously (or concurrently) applied to the pixels140, during other periods (e.g., (a), (b), (d), and (e) steps) of oneframe.

In one embodiment of the present invention, the pixel circuit 142provided in the respective pixels 140 includes three transistors M1 toM3 and one capacitor Cst.

Moreover, in one embodiment of the present invention, in considerationof the capacitance of a parasitic capacitor Coled generated by the anodeelectrode and the cathode electrode of the OLED, the coupling effect ofthe capacitor Cst and the parasitic capacitor Coled is utilized. Thiswill be described in more detail with reference to FIGS. 8A-8E.

Here, the gate electrode of the first transistor M1 is coupled to a scanline S, and the first electrode of the first transistor M1 is coupled toa data line D. The second electrode of the first transistor M1 iscoupled to a first node N1.

Here, a scan signal Scan(n) is applied to the gate electrode of thefirst transistor M1, and a data signal Data(t) is applied to the firstelectrode of the first transistor M1.

The gate electrode of the second transistor M2 is coupled to the firstnode N1, and the first electrode of the second transistor M2 is coupledto the anode electrode of the OLED. The second electrode of the secondtransistor M2 is coupled to a first power ELVDD(t) through the first andsecond electrodes of the third transistor M3. The second transistor M2serves as a driving transistor.

The gate electrode of the third transistor M3 is coupled to a controlline GC, the first electrode of the third transistor M3 is coupled tothe second electrode of the second transistor M2, and the secondelectrode of the third transistor M3 is coupled to the first powerELVDD(t).

Here, a control signal GC(t) is applied to the gate electrode of thethird transistor M3, and the first power ELVDD(t) that is varied to avoltage level (e.g., a predetermined level) is input into the secondelectrode of the third transistor M3.

In addition, the cathode electrode of the OLED is coupled to a secondpower ELVSS(t), and the capacitor Cst is coupled between the gateelectrode of the second transistor M2, at the first node, and the firstelectrode of the second transistor M2, coupled to the anode electrode ofthe OLED.

In the embodiment shown in FIG. 6, all of the first to third transistorsM1 to M3 are implemented as NMOS transistors, however, the presentinvention is not limited as such.

As described above, the pixels 140 according to the embodiment of thepresent invention are driven in the “simultaneous (or concurrent)emission scheme.”

Referring to FIG. 7, the driving of the pixels 140 is divided into areset period Reset, a threshold voltage compensation period Vth, ascan/data input period Scan, an emission period Emission, and anemission turn-off period Off for each frame, as shown in FIG. 7.

Here, the scan signals are input sequentially scan line by scan line,and the data signals are input sequentially into the pixelscorresponding thereto for the scan/data input period Scan. However, thesignals having voltage values at respective levels (e.g., predeterminedlevels), that is, the first power ELVDD(t), the scan signal Scan(n), thecontrol signal GC(t), the data signal Data(t), are collectively appliedto all of the pixels 140 that constitute the display unit 130 forperiods other than the scan/data input period Scan.

In other words, the threshold voltage compensation of the drivingtransistor provided in the respective pixels 140 and the emissionoperations of the respective pixels 140 are simultaneously (orconcurrently) implemented in all of the pixels 140 of the display unit130 for each frame.

Hereinafter, the driving in the simultaneous (or concurrent) emissionscheme according to one embodiment of the present invention will bedescribed in more detail with reference to FIGS. 8A to 8E.

FIGS. 8A to 8E are circuit diagrams and waveform diagrams for explainingthe driving of an organic light emitting display according to anembodiment of the present invention.

For the convenience of explanation, although the voltage levels of theinput signals are described using concrete numerical values, these areexemplary values for facilitating understanding but are not actualdesign values.

Moreover, in the embodiment of FIGS. 8A to 8E, it is assumed that thecapacitance of the capacitor Cst is ⅕ of the capacitance of theparasitic capacitor Coled of the organic light emitting diode.

First, referring to FIG. 8A, a Reset period is illustrated. In the Resetperiod, the data voltage applied to the respective pixels 140 of thedisplay unit 130 is reset, wherein the voltage of the anode electrode ofthe OLED is dropped below the voltage of the cathode electrode of theOLED in order that the OLED is not light-emitted.

In other words, during the Reset period, the first power ELVDD(t) isapplied at a low level (for example, −3V), the scan signal Scan(n) isapplied at a high level (for example, 11V), and the control signal GC(t)is applied at a high level (for example, 20V).

Moreover, when the threshold voltage of the second transistor M2, whichis a driving transistor, is stored, the data signal Data(t) is appliedwith a voltage value corresponding to the magnitude of the thresholdvoltage of the second transistor M2 so that the voltage at the anodeelectrode of the OLED, which is coupled to the first electrode of thesecond transistor M2, becomes about 0V.

In one embodiment, for the convenience of explanation, assuming that thethreshold voltage of the second transistor M2 is 1V, the data signalData(t) applied during the Reset period becomes 1V, as shown in FIG. 8A.

Further, the reset step in the Reset period is collectively applied toall of the pixels 140 that constitute the display unit 130 so that thesignals applied during the reset step, that is, the first powerELVDD(t), the scan signal Scan(n), the control signal GC(t), and thedata signal Data(t), are applied simultaneously or concurrently to allof the pixels 140, the signals having their voltage values set atrespective levels.

According to the application of the signals as described above, thefirst transistor M1, the second transistor M2, and the third transistorM3 are turned on.

Therefore, the voltage at 1V corresponding to the threshold voltage ofthe second transistor M2 is applied as the data signal to the first nodeN1, and a current path is formed from the first power ELVDD(t) to theanode electrode of the OLED as the second and third transistors M2 andM3 are turned on so that the voltage value at the anode electrode isdropped to −3V, which is the voltage value of the first power ELVDD(t).

Next, referring to FIG. 8B, a period, where the threshold voltage of thedriving transistor M2 provided in the pixels 140 of the display unit 130is stored in the capacitor Cst, is illustrated. In this embodiment, thedefects due to the deviation in the threshold voltage of the drivingtransistor M2, when data voltage is charged in the pixels 140, iscompensated for.

In other words, during the threshold voltage compensation period Vth,the first power ELVDD(t) is applied at a high level (for example, 15V),the scan signal Scan(n) and the control signal GC(t) are applied at ahigh level (for example, 11V and 20V), respectively, in the same manneras the Reset period, and the data signal Data(t) also maintains the samevoltage value (for example, 1V) as that in the previous Reset period.

Moreover, in the threshold voltage compensation period Vth is alsocollectively applied to the pixels 140 that constitute the display unit130. Therefore, the signals applied during the threshold voltagecompensation period Vth, including the first power ELVDD(t), the scansignal Scan(n), the control signal GC(t), and the data signal Data(t),are applied simultaneously or concurrently to all of the pixels 140, atrespective voltage values.

According to the application of the signals as described above, thefirst transistor M1, the second transistor M2, and the third transistorM3 are turned on.

However, in the case of the second transistor M2, it is turned on untilthe voltage difference Vgs between the gate electrode and the firstelectrode corresponds to the threshold voltage of the second transistorM2, and thereafter, it is turned off.

In other words, the voltage of the anode electrode of the organic lightemitting diode, which is dropped to −3V during the original Reset stepwhen a current path is formed between the first power ELVDD(t) and theanode electrode as the second and third transistors M2 and M3 are turnedon, is raised to a voltage (0V in the embodiment of FIG. 8B) that isequal to the voltage (for example, 1V) of the gate electrode of thesecond transistor M2—the threshold voltage (for example, 1V) of thesecond transistor M2.

Therefore, the first electrode of the capacitor Cst coupled to the firstnode N1 is at 1V, and the second electrode of the capacitor Cst coupledto the anode electrode of the OLED is at 0V, such that the voltagestored in the capacitor Cst becomes 1V, that is, the voltagecorresponding to the threshold voltage of the second transistor M2.

Next, referring to FIG. 8C, a scan/data input period Scan isillustrated. In the scan/data input period Scan, the scan signals areapplied, sequentially to the pixels 140, the pixels 140 being coupled tothe scan lines S1 to Sn, so that the data signals supplied to the datalines D1 to Dm are applied to the pixels 140.

In other words, in the scan/data input period Scan of FIG. 8C, the scansignals are input sequentially to the scan lines S1 to Sn, the datasignals corresponding thereto are input sequentially to the pixels 140coupled to the respective scan lines S1 to Sn, and the control signalGC(t) is applied at a low level (for example, −3V) during the period.

However, in one embodiment of the present invention, the widths of thesequentially applied scan signals are exemplarily applied at twohorizontal time 2H, as shown in FIG. 8C. In other words, the width ofthe n−1^(st) scan signal Scan(n−1) and the width of the nth scan signalScan(n) applied following thereof are applied to be overlapped by 1H.

The overlapping addresses the charge shortage phenomenon according tothe RC delay of the signal lines due to the large size of the displayunit 130.

Moreover, as the control signal GC(t) is applied at a low level, thethird transistor M3 that is an NMOS transistor in FIG. 8C is turned offso that the first power ELVDD(t) may be provided at any levels for theperiod.

In the case of the pixel shown in FIG. 8C, if the scan signal Scan(n) ata high level is applied so that the first transistor M1 is turned on,the data signal Data(t) having a voltage value (e.g., a predeterminedvoltage value) is applied to the first node N1 via the first and secondelectrodes of the first transistor M1.

Here, assuming that the voltage value of the applied data signal Data(t)is 6V, the voltage of the first node N1 is raised from the previous 1Vto 6V so that the voltage at the anode electrode becomes

${{- {Vth}} + {\frac{Cst}{{Cst} + {Coled}}\left( {{Data} - 1} \right)}} = {{- 1} + {{1/6}\left( {6 - 1} \right)}}$

due to the coupling effects between the capacitor Cst and the parasiticcapacitor Coled of the organic light emitting diode. Herein, it isassumed that the capacitance of Cst is ⅕ of the capacitance of Coled.

Consequently, the voltage having a value that reflects the thresholdvoltage of the second transistor M2 is applied to the anode electrode ofthe organic light emitting diode, that is, the first electrode of thesecond transistor M2.

However, since the third transistor M3 is not turned on during thescan/data input period, a current path is not formed between the organiclight emitting diode and the first power ELVDD(t) so that current is notsubstantially supplied to the OLED. That is, an emission is notperformed.

Next, referring to FIG. 8D, an Emission period is illustrated. In theEmission period, a current corresponding to the data voltage stored ineach of the pixels 140 of the display unit 130 is supplied to the OLEDprovided in each of the pixels 140 so that the emission is performed.

In other words, during the Emission period, the first power ELVDD(t) isapplied at a high level (for example, 15V), the scan signal Scan(n) isapplied at a low level (for example, −3V), and the control signal GC(t)is applied at a high level (for example, 20V).

Here, as the scan signal Scan(n) is applied at a low level, the firsttransistor M1 that is an NMOS transistor in FIG. 8D is turned off sothat the data signal may be supplied at any levels for the period.

Moreover, the emission step of the Emission period is also collectivelyapplied to the pixels 140 that constitute the display unit 130.Therefore, the signals applied during the emission step, that is, thefirst power ELVDD(t), the scan signal Scan(n), the control signal GC(t),and the data signal Data(t), are simultaneously or concurrently appliedto all of the pixels 140, the signals having their voltage values set atrespective levels.

According to the application of the signals as described above, thefirst transistor M1 is turned off, and the second transistor M2 and thethird transistor M3 are turned on.

As the second transistor M2 and the third transistor M3 are turned on asdescribed above, a current path is formed between the first powerELVDD(t) and the cathode electrode of the OLED. Therefore, a currentcorresponding to a Vgs voltage value of the second transistor M2, thatis, the voltage corresponding to the voltage difference between the gateelectrode and the first electrode of the second transistor M2, isapplied to the organic light emitting diode so that it is light-emittedat brightness corresponding thereto.

Here, in one embodiment of the present invention, the voltage Vgsbecomes

${{Data} + {Vth} - {\frac{Cst}{{Cst} + {Coled}}\left( {{Data} - 1} \right)}},$

andthe current flowing to the OLED corresponding to the voltage Vgs isrepresented by

Ioled=β/2(Vgs−Vth)²

so that in the embodiment as illustrated in FIG. 8D, the current flowingto the organic light emitting diode is represented as:

${Ioled} = {{{\beta/2}\left( {{Data} + {Vth} - {\frac{Cst}{{Cst} + {Coled}}\left( {{Data} - 1} \right)} - {Vth}} \right)} = {{\beta/2}\left( {{Data} - {\frac{Cst}{{Cst} + {Coled}}\left( {{Data} - 1} \right)}} \right)}}$

This current addresses the problem generated by the deviation in thethreshold voltage of the second transistor M2.

After the emission is performed on all of the pixels 140 of the displayunit 130 as described above, an emission turn-off step is performed asshown in FIG. 8E.

In other words, referring to FIG. 8E, during the emission turn-offperiod, the first power ELVDD(t) is applied at a low level (for example,−3V), the scan signal Scan(n) is applied at a low level (for example,−3V), and the control signal CG(t) is applied at a high level (forexample, 20V).

In other words, compared with the Emission period of FIG. 8D, theemission turn-off period Off is the same except that the first powerELVDD(t) is changed from the high level to the low level (for example,−3V).

In this case, a current path is formed between the anode electrode ofthe organic light emitting diode and the first power ELVDD(t) as thesecond and third transistors M2 and M3 are turned on. Therefore, thevoltage at the anode electrode is gradually dropped to −3V that is thevoltage value at the first power ELVDD(t), and consequently, the voltageof the anode electrode is dropped below that of the cathode electrode sothat the emission is turned off.

As described above, one frame is implemented through the periods shownin FIGS. 8A to 8E, and the periods are continuously repeated, therebyimplementing the following frames. In other words, after the emissionturn-off period of FIG. 8E, the reset period of FIG. 8A begins again.

FIG. 9 is a circuit diagram showing a pixel 240 according to anotherembodiment of the present invention.

Referring to FIG. 9, compared with the embodiment of FIG. 6, it isdifferent in that a transistor that constitutes a pixel circuit 242 isimplemented as a PMOS transistor.

In this case, compared with the driving timing diagrams of FIG. 7, thepolarities of a scan signal Scan(n), a control signal GC(n) are inversedas applied, a first power ELVDD(t) is fixed (for example, 0V), and thevoltage of a second power ELVSS is varied as time elapses to be in aform that is the inverse of the waveform of the first power ELVDD(t) ofFIG. 7.

Consequently, compared with the embodiment of FIG. 6, in the embodimentof FIG. 9, a difference is that the transistor is implemented as a PMOStransistor and not as an NMOS transistor, but the driving operations andthe principles thereof are similar, and thus, the detailed descriptionthereof will be omitted.

Referring to FIG. 9, the pixel 240 in one embodiment of the presentinvention includes an OLED and a pixel circuit 242 that supplies acurrent to the OLED.

The cathode electrode of the OLED is coupled to the pixel circuit 242,and the anode electrode of the OLED is coupled to the first powerELVDD(t). The OLED generates light having a brightness (e.g., apredetermined brightness) corresponding to the current supplied by thepixel circuit 242.

However, in the embodiment of FIG. 9, the pixels 240 that constitute thedisplay unit receive data signals supplied to data lines D1 to Dm whenscan signals are supplied sequentially to scan lines S1 to Sn for apartial period (the aforementioned (c) step) of one frame, but the scansignals applied to the respective scan lines S1 to Sn, the second powerELVSS applied to the respective pixels 240, and control signals appliedto respective control lines GC1 to GCn are collectively andsimultaneously (or concurrently) applied to the respective pixels 240,the signals having voltage levels at respective levels (e.g.,predetermined levels) for other periods ((a), (b), and (d) steps) of theone frame.

The pixel circuit in each of the pixels 240 includes three transistorsPM1 to PM3 and one capacitor Cst in FIG. 9.

Here, the gate electrode of the first transistor PM1 is coupled to ascan line S, and the first electrode of the first transistor PM1 iscoupled to a data line D. The second electrode of the first transistorPM1 is coupled to a first node N1.

In other words, the scan signal Scan(n) is applied to the gate electrodeof the first transistor PM1, and the data signal Data(t) is applied tothe first electrode of the first transistor PM1.

The gate electrode of the second transistor PM2 is coupled to the firstnode N1, and the first electrode of the second transistor PM2 is coupledto the cathode electrode of the organic light emitting diode. The secondelectrode of the second transistor PM2 is coupled to the second powerELVSS through the first and second electrodes of the third transistorPM3. The second transistor PM2 serves as a driving transistor.

In other words, the gate electrode of the third transistor PM3 iscoupled to the control line GC, the first electrode of the thirdtransistor PM3 is coupled to the second electrode of the secondtransistor PM2, and the second electrode of the third transistor PM3 iscoupled to the second power ELVSS.

Therefore, the control signal GC(t) is applied to the gate electrode ofthe third transistor PM3, and the second power ELVSS that is varied to apredetermined level to be provided is applied to the second electrodethereof.

In addition, the anode electrode of the OLED is coupled to the firstpower ELVDD(t), and the capacitor Cst is coupled between the gateelectrode of the second transistor PM2, that is, the first node N1, andthe first electrode of the second transistor PM2, that is, the cathodeelectrode of the OLED.

In the embodiment of FIG. 9, all of the first to third transistors PM1to PM3 are implemented as PMOS transistors.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but, on the contrary, isintended to cover various modifications and equivalent arrangementsincluded within the spirit and scope of the appended claims, andequivalents thereof.

What is claimed is:
 1. An organic light emitting display comprising: adisplay unit comprising a plurality of pixels coupled to scan lines,control lines, and data lines, wherein each of the pixels comprises anorganic light emitting diode; a control line driver for providingcontrol signals to the pixels through the control lines; and a powerdriver for applying a power, at different levels, to the pixels during aplurality of periods of one frame, wherein the power comprises a firstpower and a second power applied to the pixels, wherein the controlsignals at a turn-on level are concurrently provided to respectiveswitches electrically coupled between the second power and organic lightemitting diodes of the pixels, wherein the power is simultaneouslyprovided to each of the pixels, wherein the plurality of periods of oneframe comprise a reset period, a threshold voltage sensing period, ascan period, an emission period, and an emission turn-off period,wherein the second power is applied at a high level during the resetperiod and the emission turn-off period, and wherein the second power isapplied at a low level during the threshold voltage sensing period andthe emission period.
 2. The organic light emitting display as claimed inclaim 1, wherein the second power is applied at a level higher than thelow level and lower than the high level during the scan period.
 3. Theorganic light emitting display as claimed in claim 1, furthercomprising: a scan driver for supplying scan signals to the pixelsthrough the scan lines; a data driver for supplying data signals to thepixels through the data lines; and a timing controller for controllingthe control line driver, the power driver, the scan driver, and the datadriver.
 4. The organic light emitting display as claimed in claim 3,wherein the scan signals are applied sequentially to the scan lines fora partial period of the periods of one frame and are appliedconcurrently to the scan lines during the periods except for the partialperiod.
 5. The organic light emitting display as claimed in claim 4,wherein widths of the sequentially applied scan signals are applied attwo horizontal times, two adjacently applied ones of the scan signalsbeing applied to be overlapped with each other by one horizontal time.6. The organic light emitting display as claimed in claim 4, wherein thedata signals are applied sequentially to the pixels scan line by scanline corresponding to the sequentially applied scan signals and areconcurrently applied to all of the pixels through the data lines duringthe periods except for the partial period.
 7. The organic light emittingdisplay as claimed in claim 1, wherein each of the pixels furthercomprises: a first transistor having a gate electrode coupled to a scanline of the scan lines, a first electrode coupled to a data line of thedata lines, and a second electrode coupled to a first node; a secondtransistor having a gate electrode coupled to the first node, a firstelectrode, and a second electrode; a third transistor having a gateelectrode coupled to a control line of the control lines, a firstelectrode coupled to the second electrode of the second transistor, anda second electrode coupled to the second power; and a capacitor coupledbetween the gate electrode of the second transistor and the firstelectrode of the second transistor, wherein the organic light emittingdiode has an anode electrode coupled to the first power and a cathodeelectrode coupled to the first electrode of the second transistor. 8.The organic light emitting display as claimed in claim 7, wherein thefirst to third transistors are PMOS transistors.
 9. The organic lightemitting display as claimed in claim 1, wherein a voltage of the poweris varied after each of the plurality of periods of one frame.
 10. Adriving method of an organic light emitting display having a powerdriver for applying a first power and a second power, at differentlevels, to pixels during a plurality of periods of one frame, the methodcomprising: (a) resetting data voltages applied to a plurality of pixelsby concurrently applying the second power at a high level, scan signals,control signals, and data signals having voltage values at respectivelevels, to all of the pixels that constitute a display unit, whereineach of the pixels comprises an organic light emitting diode; (b)storing a threshold voltage of a driving transistor included in each ofthe pixels by concurrently applying the second power at a low level, thescan signals, the control signals, and the data signals having thevoltage values at the respective levels to all of the pixels; (c)applying the scan signals sequentially to the pixels coupled to scanlines of the display unit and applying the data signals to the pixelsscan line by scan line corresponding to the sequentially applied scansignals, and concurrently applying the second power at a level lowerthan the high level; (d) light-emitting all of the pixels, concurrently,at brightnesses corresponding to the data voltages stored in the pixelsby concurrently applying the second power at the low level, the scansignals at a logic low level, the control signals at a logic high level,and the data signals having the voltage values at the respective levelsto all of the pixels, and (e) turning off emission of the pixels byconcurrently applying the second power at the high level and the firstpower, the control signals, and the data signals having the voltagevalues at the respective levels, to all of the pixels and thusincreasing a voltage of a cathode electrode of the organic lightemitting diode included in each of the pixels, wherein each of thecontrol signals is concurrently provided with each of the other controlsignals, at a turn-on level, directly to a transistor electricallycoupled between the second power and the organic light emitting diode ina corresponding one of the pixels.
 11. The driving method of the organiclight emitting display as claimed in claim 10, wherein one frame isimplemented through (a) to (e).
 12. The driving method of the organiclight emitting display as claimed in claim 11, wherein the one frame isa progressively progressed frame and comprises an n^(th) frame fordisplaying a left-eye image and an (n+1)^(th) frame for displaying aright-eye image.
 13. The driving method of the organic light emittingdisplay as claimed in 12, wherein an entire time between an emissionperiod of the n^(th) frame and an emission period of the (n+1)^(th)frame is synchronized with a response time of a pair of shutter glasses.14. The driving method of the organic light emitting display as claimedin claim 10, wherein each of the pixels comprises: a first PMOStransistor having a gate electrode coupled to a scan line, a firstelectrode coupled to a data line, and a second electrode coupled to afirst node; a second PMOS transistor having a gate electrode coupled tothe first node, a first electrode, and a second electrode; a third PMOStransistor having a gate electrode coupled to a control line, a firstelectrode coupled to the second electrode of the second PMOS transistor,and a second electrode coupled to the second power; and a capacitorcoupled between the gate electrode of the second PMOS transistor and thefirst electrode of the second PMOS transistor, wherein the organic lightemitting diode having an anode electrode coupled to the first power anda cathode electrode coupled to the first electrode of the second PMOStransistor.
 15. The driving method of the organic light emitting displayas claimed in claim 14, wherein, in (a), the second power is applied ata high level, the scan signal is applied at a low level, and the controlsignal is applied at a low level.
 16. The driving method of the organiclight emitting display as claimed in claim 14, wherein, in (b), thesecond power is applied at a low level, and the scan signal and thecontrol signal are applied at a low level, respectively.
 17. The drivingmethod of the organic light emitting display as claimed in claim 14,wherein, in (c), the control signal is applied at a high level.
 18. Thedriving method of the organic light emitting display as claimed in claim14, wherein, in (c), widths of the sequentially applied scan signals areapplied at two horizontal times, adjacently applied ones of the scansignals being applied to be overlapped with each other by one horizontaltime.
 19. The driving method of the organic light emitting display asclaimed in claim 10, wherein the voltage value of the second powervaries after each of plurality of periods of one frame.